Samples of the lichen Parmelia sulcata Taylor were collected in the vicinity of 17 air pollution monitoring stations in the northern part of Switzerland and its bordering area. Net photosynthesis, dark respiration, and the content of [35S]-sulphate and [35S]-protein after cultivation with 35SO42−, as well as the chlorophyll and protein contents were measured. Mean values of dark respiration and protein content were not significantly different in the plant material from the various locations. Most of the mean values of net photosynthesis differed less than the average standard deviation. The rates of sulphate uptake and protein synthesis were lowest and chlorophyll content was highest at the most polluted sites. The values differed by a factor of 3.5-7 between the various locations. Multiple regression analysis gave a linear correlation between the three physiological parameters [35S]-sulphate, [35S]-protein and chlorophyll content and a combination of the annual mean concentrations of the air pollutants NO, NO2, SO2 and O3. The highest multiple correlation coefficient (R2) was estimated for chlorophyll (0-84). Its linear correlation coefficient (r) with NO2 alone was 0.91, and with SO2 alone 0.85.